The present invention relates generally to the automotive chain drive art and, more particularly, to a chain tensioner apparatus useful in confined spaces for applying a tensioning force to a chain traveling therepast. Several prior patents describe various chain tensioner devices that include a chain engaging blade or shoe member, typically molded from a resinous plastic material, having a metal spring installed therein to provide the shoe sub-assembly with the necessary rigidity and damping characteristics while taking advantage of the flexibility, low friction, and good wear properties of the plastic shoe. For example, commonly assigned U.S. Pat. No. 5,286,234, the disclosure of which is hereby expressly incorporated by reference, discloses a chain tensioner in which a metal spring is inserted in the longitudinal slot of the shoe. A bracket is provided for operably affixing the spring/shoe sub-assembly to an engine block. A first (pivot) end of the spring/shoe sub-assembly is pivotably secured to the bracket by a pin or fastener. The opposite (free) end of the spring/shoe sub-assembly is supported on a ramp. The bracket defines an up-turned tab portion adjacent the ramp. The tab portion, ramp and base wall of the bracket cooperate to define a channel that holds the free end of the spring/shoe sub-assembly but that allows for reciprocation on same on the ramp. The bracket thus maintains the shoe in its proper position with respect to the plane of the chain path while permitting sliding motion of the shoe free end on the ramp along with the related rotational movement of the shoe at the pivot end. An object of the arrangement disclosed in the ""234 patent is to retain the spring within the shoe spring slot while keeping the shoe in its proper position. In particular, the spring is properly retained in that its movement is limited in one direction by the side wall of the bracket and in the opposite direction by the shoe, itself.
U.S. Pat. No. 5,711,732, the disclosure of which is hereby expressly incorporated by reference, discloses a chain tensioner wherein the bracket is not used to retain the spring. Such an arrangement is required because applications exist where it is not feasible for the bracket base wall to be used for spring retention purposes. Spring retention for the device disclosed in the ""732 patent is achieved by mechanically interlocking the spring to the shoe. In one arrangement, the spring defines open slots at its opposite ends. The shoe defines a longitudinal slot that opens in a rear face thereof for receiving the spring, and a retaining ridge is defined by a central projection at each end of the longitudinal slot. The retaining ridges at the opposite longitudinal ends of the slot respectively engage the slots defined in opposite ends of the spring so that the spring is releasably and fixedly secured in the slot. As with the ""234 patent, the slot is closed by a front face of the shoe so that the spring is prevented from exiting the slot in a first direction by the front face of the shoe and in a second direction by the mechanical interlock arrangement just described.
In an alternative embodiment disclosed in the ""732 patent, a central rib feature (male adapter) is provided at one end of the slot and accords positive spring retention in the shoe while at the same time beneficially permitting a more narrow part width at this end of the shoe (see FIG. 17). Notably, this central rib is connected to, and extends from, the top surface of the slot to the bottom surface, i.e., the rib spans the slot. The T-section provided by this central rib provides necessary structural integrity for the shoe and spring sub-assembly.
The blade-type mechanical tensioners disclosed in the ""234 and ""732 patents have been found to be highly effective and have enjoyed widespread commercial success. However, finite element analysis and empirical data have shown the existence of a high stress area at the end of the central rib and the blade juncture at the pivot end (where the central rib spans the slot), and the stress levels can be particularly high when the blade width is narrow and the blade length is short. For some applications having a more restricted width and length packaging envelope, the above described blade-type chain tensioners may not have the capability to apply a required tensioning force, or may not have the required blade flexure and strength. Accordingly, it has been deemed desirable to develop a new and improved blade-type chain tensioner that will function properly in a more confined environment and that will overcome the forgoing deficiencies and others while providing better overall performance.
In accordance with a first aspect of the present invention, a blade and spring sub-assembly apparatus for use in a chain tensioner of a chain drive system is provided. The apparatus comprises a blade having first and second opposite end portions joined together by a central portion. The blade defines an exterior chain guide surface adapted for slidingly abutting an associated chain of an associated chain drive system. A tensioning spring is connected to the blade and has opposite first and second ends located respectively adjacent the first and second opposite end portions of the blade. The spring contacts and exerts a biasing force on the central portion of the blade. A hub is defined by the first end portion of the blade. The hub is connected to the central portion of the blade by a first end wall and defines a through-bore adapted for receipt of an associated pin for pivotably connecting the blade to an associated mounting bracket. A rib projects outwardly away from the first end wall. The rib comprises a first end located adjacent the central portion of the blade and a second end located adjacent the hub.
In accordance with another aspect of the present invention, a chain tensioner apparatus comprises a mounting bracket adapted for connection to an associated engine block. The mounting bracket defines a pivot point and a support surface. The chain tensioner apparatus further includes a blade comprising: (i) first and second opposite end portions joined together by a central portion; (ii) a hub defined by the first end portion; and, (iii) a first end wall connecting the hub to the central portion. The hub of the blade is pivotably connected to the bracket at the pivot point and the second end of the blade abuts the support surface. The blade defines an exterior chain guide surface adapted for slidingly abutting an associated chain of an associated chain drive system. The chain tensioner apparatus further includes a tensioning spring connected to the blade, the spring having opposite first and second ends located respectively adjacent the first and second opposite end portions of the blade. The spring contacts and exerts a biasing force on the central portion of the blade. A rib projects outwardly away from the first end wall of the blade. The rib comprises a first end located adjacent the central portion of the blade and a second end located adjacent the hub.
One advantage of the present invention resides in the provision of a new and improved blade-type mechanical chain tensioner exhibiting improved strength, durability, and effectiveness in a confined application.
Another advantage of the present invention resides in the provision of a blade-type mechanical chain tensioner wherein the effective length of the spring-receiving slot and the effective length of the flexing portion of the blade (shoe) is maximized without undesirably weakening the shoe.
Still another advantage of the present invention resides in the provision of a blade-type mechanical chain tensioner wherein the spring can be retained in the slot defined by the shoe by either a mechanical interlock with the shoe or by the bracket to which the shoe is connected.
Still other benefits and advantages of the present invention will become apparent to those of ordinary skill in the art to which the invention pertains upon reading this specification.